JP2018021852A - Method for measuring concentration of metal impurity in polycrystalline silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can eliminate contaminations of a metal impurity in polycrystalline silicon from the outside and analyze the metal impurity sensitively and accurately.SOLUTION: According to the method, polycrystalline silicon as a measurement target is subjected to single crystalline growth by a FZ method, and a final solidified part is collected from the obtained silicon single crystal rod and is exposed to degradable vapor of silicon, specifically to vapor of fluonitric acid so that residues of degradation are obtained. After that, the residues are dissolved into a recovery solution and the metal amount is measured, and the determined metal amount is converted into the concentration of the polycrystalline silicon as the measurement target.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for measuring the concentration of metal impurities contained in polycrystalline silicon. Specifically, the present invention analyzes a silicon single crystal grown by the FZ method using polycrystalline silicon to be measured, and is contained in the polycrystalline silicon. The present invention relates to a method for measuring a metal impurity concentration with high sensitivity.

  With the increase in diameter of silicon wafers and the high integration of devices, reduction of metal impurities in silicon wafers is required. For this reason, it is necessary to reduce the metal impurities in the polycrystalline silicon that is the raw material of the silicon wafer, and accordingly, an analytical technique for evaluating the metal impurity concentration in the polycrystalline silicon should be established. Is desired.

  Conventionally, chemical analysis and activation analysis are known as methods for quantifying the impurity concentration of polycrystalline silicon. However, since it has low sensitivity and is easily affected by external contamination, it has been difficult to fully quantify it for polycrystalline silicon having an extremely small impurity content.

  For this reason, as a method for analyzing the carbon and dopant impurity concentrations contained in polycrystalline silicon with high sensitivity, for example, “High Purity Polycrystalline Silicon Standard Standard” discloses the following method. That is, first, a round bar is cut out from the straight body portion of the polycrystalline silicon rod in the diameter direction, and then the polycrystalline silicon rod is monocrystallized by the FZ (Float-Zone) method. A sample is cut out from the straight body and various impurities are measured by a photoluminescence method. And it is the method of carrying out theoretical calculation based on the obtained measured value, and converting into the amount of impurities contained in the original polycrystalline silicon rod. (Refer nonpatent literature 1). On the other hand, for the analysis of metal impurities, since the segregation coefficient of metal is small, the amount contained in the sample cut out from the silicon single crystal rod body is very small, and the above method is sufficiently satisfactory for high sensitivity requirements. It is difficult to obtain a good result. Therefore, it was a usual method to analyze the surface portion of the polycrystalline silicon by immersing it in a hydrofluoric acid aqueous solution.

  Under these circumstances, it has been proposed to use the final solidified portion (tail portion) of the silicon single crystal rod produced by the FZ method as a measurement sample (see Patent Documents 1 and 2). That is, since the metal impurities contained in the measurement sample are concentrated at a high concentration in the final solidified portion, the analysis sensitivity of the metal impurities can be increased by collecting and analyzing the impurities. is there. In this method, the metal impurity concentration in the final solidified part is analyzed by immersing it in an aqueous solution of hydrofluoric acid to decompose the final solidified part to extract the metal, and once evaporating this recovered liquid to dryness, the residue is removed. It is performed by redissolving in an acid solution and performing chemical analysis by inductively coupled plasma mass spectrometry or the like.

"Electronic Information Technology Industry Information Standard JEITA EM-3601A Standard Standard for High Purity Polycrystalline Silicon", Japan Electronics and Information Technology Industries Association, September 2004

Japanese Patent Laid-Open No. 5-26803 Japanese Patent Laid-Open No. 11-304791

  However, even if the final solidified part of the silicon single crystal rod obtained by the FZ method is the object of analysis, the conventional proposed method is not sufficient for the analysis sensitivity, and it is required to improve it to a higher sensitivity. It was.

  In view of the above problems, the present inventors have continued intensive studies. As a result, even if the final solidified portion of the silicon single crystal rod obtained by the FZ method is used as an analysis sample, the reason why the analytical sensitivity is not sufficiently high is that the extraction of metal from the final solidified portion is The knowledge by being immersed in nitric acid aqueous solution was obtained. That is, when a metal impurity is also contained in the hydrofluoric acid aqueous solution, in order to decompose the silicon single crystal forming the final solidified portion, it must be immersed in a considerable amount of the hydrofluoric acid aqueous solution, thereby The main cause was the occurrence of external contamination of impurities, making the analysis with high sensitivity difficult. And based on this knowledge, for the extraction of metal impurities from the final solidified part, if the final solidified part is exposed to silicon decomposable vapor, it is found that the external contamination can be greatly suppressed, The present invention has been completed.

  That is, the present invention is a method for measuring the concentration of metal impurities contained in polycrystalline silicon, which is obtained by growing a single crystal by the FZ method using polycrystalline silicon to be measured, The solidified portion is collected, and then the final solidified portion is exposed to silicon decomposable vapor to obtain a decomposition residue, which is then dissolved in a recovered solution to measure the amount of metal, and the concentration of polycrystalline silicon to be measured This is a method for analyzing a metal impurity in polycrystalline silicon.

  According to the present invention, metal impurities contained in polycrystalline silicon can be analyzed with high sensitivity and high accuracy while suppressing the influence of external contamination.

FIG. 1 is a schematic diagram showing a typical embodiment in which the final solidified portion collected from a silicon single crystal rod obtained by the FZ method is exposed to silicon decomposable vapor (hydrofluoric acid vapor) in the present invention. FIG. 2 is a schematic diagram showing a typical embodiment of a method for obtaining a silicon single crystal rod by the FZ method. FIG. 3 is a schematic view showing a state of a silicon single crystal rod manufactured by the FZ method.

  In the present invention, the polycrystalline silicon for analyzing the amount of metal impurities is not particularly limited, and usually from the straight body portion of the polycrystalline silicon rod manufactured by the Siemens method in the diametrical direction including the precipitation core. The cut polycrystalline silicon rod is the target. That is, by analyzing the amount of metal contained in the polycrystalline silicon rod, the amount of metal impurities in the polycrystalline silicon rod obtained by the Siemens method obtained by cutting this can be obtained. Here, the Siemens method is a method of contacting polycrystalline silicon on the surface of the silicon core wire by a CVD (Chemical Vapor Deposition) method by bringing a silane source gas such as trichlorosilane or monosilane into contact with the heated silicon core wire. It is a method of growing (depositing).

  Thus, the diameter of the polycrystalline silicon rod cut out from the straight body portion of the polycrystalline silicon rod is generally selected from the range of 15 to 25 mm, but “Electronic Information Technology Industry Information Standard JEITA EM-3601A It is particularly preferred that the thickness is 19 ± 1 mm in accordance with the “crystalline silicon standard specification”.

  Further, even if the polycrystalline silicon to be measured is not rod-shaped but granular, it is filled into a cylindrical body and heated in a band shape from the circumferential direction to obtain at least a part of the granular polycrystalline silicon. By integrating by fusion sintering, a polycrystalline silicon rod can be formed and applied to single crystal growth by the FZ method. The outline of this method may be carried out according to the method described in JP-A-11-304791, for example. The material of the cylinder may be non-conductive, but ceramic such as alumina, silica, silicon nitride is usually used. In particular, transparent quartz glass is preferably used because the inside can be seen through.

  Examples of granular polycrystalline silicon include crushed polycrystalline silicon rods produced by the Siemens method, granular polycrystalline silicon obtained by fluidized bed reaction, and the like. The particle diameter of the granular polycrystalline silicon is preferably 0.1 to 10 mm, particularly 1 to 5 mm, expressed as a major axis, from the viewpoint of good operability.

  In the analysis method of the present invention, single crystals of these polycrystalline silicon are grown by the FZ method to obtain a silicon single crystal rod. The FZ method is an abbreviation for the Float-Zone method, and is a method in which a raw material polycrystal is partially heated and melted using a high-frequency induction heating coil and a single crystal is grown by moving the melting zone. The operation may be in accordance with the method described in “JEITA EM-3601A” or “JIS H 0615 Method for Measuring Impurity Concentration in Silicon Crystal by Photoluminescence” cited in this standard. With reference to the perspective view of FIG. 2, a typical mode for obtaining a silicon single crystal rod by the FZ method will be described.

  In FIG. 2, the prepared polycrystalline silicon rod 9 is set so that the lower end thereof is in the vicinity of the high-frequency induction heating coil 10. A high frequency is applied to the high frequency induction heating coil 10 to heat the lower end of the polycrystalline silicon rod 9 to a temperature sufficient for induction heating. When high frequency is applied to the lower end of the polycrystalline silicon rod 9, it melts. The lower end of the polycrystalline silicon rod 9 may be preheated by a carbon heater before being heated by the high frequency induction heating coil 10.

  After the lower end of the polycrystalline silicon rod 9 is heated, the seed crystal 11 is moved from below and the upper end of the seed crystal 11 is immersed in the melt formed at the lower end of the polycrystalline silicon rod 9 to be melted. After the upper end of the seed crystal 11 is melted, the polycrystalline silicon rod 9 and the seed crystal 11 are simultaneously moved downward at a predetermined speed, generally 1 to 5 mm / min. A single crystal grows sequentially on the upper end of the seed crystal 11.

  As shown in FIG. 3, after the silicon single crystal 12 grows to a predetermined length, for example, 100 to 300 mm, the polycrystalline silicon rod 9 is stopped from moving downward and moved to the upper portion to thereby move the polycrystalline silicon rod 9. The melt formed between the silicon single crystal 12 and the silicon single crystal 12 is cut, and the melt formed between the polycrystalline silicon rod 9 and the single crystal just before the cutting is held at the upper end of the single crystal and then solidified. Thus, the so-called final solidified portion 4 is obtained. The polycrystalline silicon rod 9 is formed so that the amount of the melt formed between the polycrystalline silicon rod 9 and the silicon single crystal 12 immediately before cutting is a predetermined amount, generally a triangular pyramid having a height almost equal to the diameter. Before the melt formed between the silicon single crystal 12 and the silicon melt is cut, the high frequency output is adjusted in advance.

  The production of the silicon single crystal rod by the FZ method is preferably performed in a clean inert gas atmosphere, and the obtained silicon single crystal rod is preferably stored in a clean inert gas or in a vacuum state. .

  When subjected to the FZ method, the surface of the polycrystalline silicon to be measured is preferably cleaned immediately before in order to eliminate metal contamination on the surface. As this surface cleaning, for example, a method of rinsing with ultrapure water after etching cleaning with a hydrofluoric acid aqueous solution and blowing with a clean gas can be mentioned. Another method of such surface cleaning is also defined in the JIS H 0615. The polycrystalline silicon whose surface has been cleaned is preferably stored under a clean inert gas or in a vacuum state while waiting for FZ.

  It is desirable to carry out the FZ method by a method that is not contaminated with impurities as much as possible. From this point of view, it is preferable to use a silver coil as the high-frequency induction heating coil. That is, in the FZ method, the high-frequency induction heating coil that is installed surrounding the polycrystalline body is likely to contaminate the silicon single crystal rod inserted into the inner space. At this time, if the high-frequency induction heating coil is made of copper or the like that is widely used, copper is not desirable because it is a metal that is desired to avoid contamination as much as possible in polycrystalline silicon as will be described later. On the other hand, when the high-frequency induction heating coil is made of silver (particularly, pure silver having a purity of 99.99% by mass or more), such external contamination by highly harmful metals is preferably suppressed. In the FZ furnace that accommodates the high-frequency induction heating coil, it is preferable that a clean inert gas always flows. Further, during the melting of the polycrystalline silicon, the number of particles of 0.5 μm or more is preferably 100 or less in 2.8 L in the measurement of the outlet of the furnace.

  The final solidification part of the silicon single crystal rod is preferably manufactured by leaving the final melt zone on the single crystal side and quickly separating the upper polycrystal. In the silicon single crystal rod thus obtained by the FZ method, metal impurities are concentrated by segregation in the final solidified portion. Therefore, in the present invention, the final solidified portion is separated from the silicon single crystal rod and the amount of metal contained therein is measured to obtain the amount of metal impurities contained in the polycrystalline silicon to be measured.

  Here, separation of the final solidified portion from the silicon single crystal rod may be performed as appropriate. For example, cutting using a metal blade causes metal contamination of the cut surface. For this reason, it is preferable to collect by hitting with a resin hammer. The mounting table for hitting is also preferably made of silicon, particularly polycrystalline silicon, in order to reduce external contamination. These hammers and mounting tables are preferably provided after etching and cleaning as appropriate.

  The amount of the final solidified portion collected is preferably 0.1% by mass to 5% by mass, particularly preferably 0.5% by mass to 3% by mass, based on the total weight of the silicon single crystal rod. If the final solidified part is less than 0.1% by mass, the part becomes minute, so that the operability of collection is deteriorated, and if it is 5% by mass or more, the operability at the time of decomposition deteriorates. It is not preferable for quantitative determination. It is preferable that the collected final solidified portion is washed with hydrofluoric acid, hydrochloric acid, hydrogen peroxide acid, or a mixed acid thereof to remove only the adhesion contamination on the outermost surface and used for the next step.

  The final solidified portion collected in this way decomposes the silicon single crystal constituting the metal, recovers metal impurities, and analyzes the amount. The present invention has the greatest feature in that the metal impurities are recovered from the final solidified portion by exposing the final solidified portion to silicon decomposable vapor. Thus, by exposing to a decomposable vapor | steam, a silicon single crystal decomposes | disassembles and a decomposition residue is obtained, this is melt | dissolved in a collection | recovery liquid, The metal amount is measured.

  That is, when the final solidified portion is immersed in a silicon decomposition solution (typically an aqueous solution of hydrofluoric acid) as in the prior art, the decomposable solution used is a high-purity product. However, a considerable amount of metal impurities are contained, which affects the analysis of trace metals contained in the final solidified portion. On the other hand, if the silicon decomposable vapor is used as described above, even if the vapor generation source liquid contains a certain amount of metal impurities, the amount accompanying the vapor generated in the future. Therefore, the influence of external contamination can be greatly reduced when measuring metal impurities contained in the final solidified portion.

  Here, specific examples of the decomposable vapor of silicon include vapors of acid solutions such as hydrofluoric acid, hydrofluoric acid, ammonium fluoride, and aqua regia, and particularly preferred is hydrofluoric acid vapor. The nitric acid vapor is preferably generated by heating a mixed solution containing 15 to 25% by mass of hydrofluoric acid and 30 to 40% by mass of nitric acid to a boiling point of 60 to 90 ° C., more preferably for electronic industry or more. Vapor obtained by heating a solution obtained by mixing 18 to 22% by mass hydrofluoric acid and 34 to 38% by mass nitric acid on a heating medium such as a hot plate is particularly excellent in silicon decomposability. Therefore, it is preferable. Moreover, as a vapor | steam ratio, it is preferable that a hydrofluoric acid will be 50-70 mass% with respect to the total mass of a hydrofluoric acid and nitric acid.

  Considering the little contamination from the outside air, it is preferable that the final solidification part is stored in a closed container for decomposition, and the above decomposable vapor is also generated in the closed container and allowed to act on the final solidification part. A typical embodiment in which the final solidified portion is exposed to silicon decomposable vapor using such a sealed container will be described with reference to FIG. In this embodiment, hydrofluoric acid vapor is used as the decomposable vapor of silicon.

  In FIG. 1, the final solidified part disassembling sealed container 1 is composed of a container main body 2 having an upper opening and a sealing lid 3 covering the opening, and a beaker mounting table 8 is provided at the center of the container main body 2. A beaker 5 in which the final solidified portion 4 is housed is placed thereon. A hydrofluoric acid aqueous solution 6 is accommodated at a position lower than the beaker 5 at the bottom of the container body 2. Further, the ceiling of the sealing lid 3 is preferably inclined in an umbrella shape (conical shape) in order to prevent the condensed droplets of the decomposable vapor adhering from dropping into the beaker 5. The airtight container 1 is placed on a hot plate 7 and heated to a suitable temperature for generating the fluorinated nitric acid vapor, thereby filling the airtight container 1 with the fluoric nitric acid vapor, and the final solidified portion 4 stored in the beaker 5. The silicon may be decomposed at.

  The material of the sealed container is preferably an acid-resistant and pressure-resistant material, and is made of a fluororesin such as tetrafluoroethylene resin (PTFE) or a copolymer resin of tetrafluoroethylene and perfluoroalkoxyethylene (PFA). preferable. The time for which the final solidified portion is exposed to the decomposable vapor is determined as a time required to sufficiently decompose the silicon single crystal constituting the final solidified portion, and is generally selected from 10 to 50 hours.

  Thus, by decomposing the silicon single crystal constituting the final solidified portion, a decomposition residue in which the metal impurities contained in the final solidified portion are concentrated is generated in the beaker 5. The obtained decomposition residue is preferably dried by heating and then used for dissolution in the recovered liquid. In addition, white solids may be contained in the decomposition residue. In this case, before or after the decomposition, it is suppressed by adding sulfuric acid or aqua regia to dryness and introducing the recovered liquid into the measuring device. It is preferable because it can prevent variation in quantity.

Examples of the recovery solution for dissolving the decomposition residue include nitric acid, hydrochloric acid, aqua regia, sulfuric acid and the like, and sulfuric acid from which a high-purity product can be obtained is particularly suitable. The concentration of the acid is preferably 0.05 to 0.3% by mass from the viewpoint of dissolving the decomposition residue. Dissolution is performed after the decomposition residue is allowed to cool, and the amount of recovered liquid is accurately measured with a pipette or the like. The amount of liquid recovered is sufficient for the measurement of metals.
100-500 μl is preferred.

The method for analyzing the amount of metal is not particularly limited, but usually, atomic absorption or inductively coupled plasma mass spectrometry is applied. The specific measurement operation in these analytical methods may follow a conventional method. Based on the obtained measurement value, the metal impurity concentration of the polycrystalline silicon to be measured is calculated. The method is
Concentration (pptw) = (Measured value from final solidified part−operation blank) (pg / ml) × recovered liquid (ml) ÷ total weight of silicon single crystal rod (g)
According to. Here, the said operation blank is a measured value of the control test which measured the metal amount using the collection | recovery liquid which does not dissolve the decomposition residue of the final solidification part.

In polycrystalline silicon, the metal impurity to be measured is preferably as small as the segregation coefficient, and for example, an element having a segregation coefficient of less than 1 is particularly preferable. These elements include Li, Cu, Ag, Au, Zn, Cd, Cr, Al, Ga, In, Th, Sn, As, Bi,
Mg, Fe, Co, Ni, Ta, Ti and the like can be mentioned. In particular, at least one selected from Cu, Ni, and Fe is preferable because of its influence on electrical characteristics. Among these, Cu is an element that is strongly required to be reduced because of its very fast diffusion in silicon, and the effect of increasing the sensitivity in the measurement method of the present invention is also remarkable and is particularly preferable.

  The limit of quantification of polycrystalline silicon is generally 10 ppbw or less for Fe, Ni, and Cu, and 100 pptw is also possible when performed with great care.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
Polycrystalline silicon for FZ in the diametrical direction including the precipitation core from an arbitrary position in the longitudinal direction of the straight body portion of the polycrystalline silicon rod manufactured by the Siemens method using trichlorosilane as a raw material gas. A stick was cut out. After etching the cut surface of a 120 mm long polycrystalline silicon rod with an aqueous hydrofluoric acid solution mixed with 10 ml of 50 mass% hydrofluoric acid and 40 ml of 61 mass% nitric acid for each electronic industry, the metal impurities are 1 ptw or less. Rinse with ultrapure water. Water droplets on the polycrystalline silicon rod were blown with Ar gas, sucked in a vacuum desiccator, and stored until immediately before the production of the silicon single crystal rod by the FZ method.

  A high-frequency induction heating coil made of pure silver was used as an apparatus for manufacturing a silicon single crystal rod by the FZ method. Using this manufacturing apparatus, a silicon single crystal rod was manufactured by the FZ method using a polycrystalline silicon rod cut out from the polycrystalline silicon rod as a raw material. Specifically, first, the polycrystalline silicon rod was set so that the lower end thereof was in the plane of the high frequency induction heating coil. In the initial stage of heating, the carbon plate is heated with a high-frequency induction heating coil at an output of 7.5 KW (frequency is 2 MHz) until the rod-shaped silicon reaches a temperature sufficient for induction heating by the radiant heat from the carbon plate. A polycrystalline silicon rod was radiantly heated. After confirming that the high frequency was applied to the polycrystalline silicon rod, the carbon plate was removed, and at the same time, the high frequency output was lowered from 7 KW to 4 KW so that the lower end 10 mm of the polycrystalline silicon rod was in a molten state. A seed single crystal having a length of 75 mm and a side of 3.5 mm square is moved from below, and its upper end is immersed in a melt formed at the lower end of the polycrystalline silicon rod to melt it. Was brought into a bonded state via the melt.

  After making the above state, the polycrystalline silicon rod and the seed crystal were simultaneously moved downward at a speed of 2 mm / min and 5 mm / min, respectively, and the heating zone was relatively raised. During the movement of the heating zone, the high frequency output was maintained at 4.5 KW so that the amount of the melt did not change. During melting of the polycrystalline silicon rod, clean argon gas was constantly flowed at 20 L / min in the FZ furnace, and the number of particles of 0.5 μm or more was maintained at 50 or less in 2.8 L in the furnace outlet measurement. . After a 100 mm long single crystal was grown above the seed crystal, the high frequency output was lowered from 4 KW to 2.5 KW, the amount of the melt was reduced, and the downward movement of the silicon single crystal rod was stopped. The melt formed between the silicon single crystal rod and the single crystal is cut, and the melt formed between the silicon single crystal rod and the single crystal is held at the upper end of the single crystal immediately before cutting. After solidifying to produce a so-called final solidified portion, it was allowed to cool in a furnace to produce a silicon single crystal rod having a diameter of 12 mm, a length of 220 mm, and 50.2 g.

  Next, 0.5 g of the final solidified portion of this silicon single crystal rod was separated and collected by hitting with a Teflon (registered trademark) hammer on a polycrystalline silicon stand. The surface of the final solidified portion is washed with a mixed solution of 5% by mass hydrofluoric acid, 5% by mass hydrochloric acid, and 5% by mass hydrogen peroxide, and rinsed with ultrapure water having a metal impurity of 1 pptw or less. It was stored in the beaker 5 of the closed container 1 for final solidification part decomposition shown in FIG. Further, 50 ml 50% hydrofluoric acid and 70 ml 61% nitric acid nitric acid for each electronic industry are put in the bottom of the container body 2, and then the upper surface opening of the container body 2 is shielded by the sealing lid 3. The container 1 was placed on a hot plate set at 140 ° C.

  Thereby, the inside of the sealed container 1 was filled with hydrofluoric acid vapor, and the final solidified portion in the beaker 5 was exposed to the hydrofluoric acid vapor, and the decomposition proceeded. This decomposition operation was continued for 24 hours, and a decomposition residue was obtained at the bottom of the container body 2. The beaker 5 was further heated and dried on a hot plate and then allowed to cool.

  After standing to cool, the decomposition residue at the bottom of the beaker 5 was dissolved and recovered in 0.5 ml of a recovery solution composed of 0.1% by mass sulfuric acid. The concentration of each metal element of Cu, Ni, and Fe in the recovered liquid was measured by an inductively coupled plasma mass spectrometer. In addition, it is carried out in the same manner without accommodating anything in the beaker 5 of the sealed container 1, and blank measurement for measuring the concentration of each metal element of Cu, Ni, and Fe is also carried out five times, and the measurement obtained. The lower limit of quantification for each metal element was determined from the value 10σ.

From the above analysis results, the following calculated concentration (pptw) = (measured value from the final solidified part−operation blank) (pg / ml) × recovered liquid (ml) ÷ total weight of silicon single crystal rod (g)
Thus, the concentration of metal impurities contained in the polycrystalline silicon rod cut out from the polycrystalline silicon rod was determined. The results are shown in Table 1.

Comparative Example 1
In Example 1, as the closed container 1 for final solidification part decomposition, a container in which the beaker holding base 8 is not provided in the center of the bottom of the container body 2 and the beaker 5 is not installed is used. The final solidified part collected from the container body 2 is directly accommodated in the bottom of the container body 2 and the aqueous hydrofluoric acid solution (50 ml of 50% by mass hydrofluoric acid for each electronic industry and 70 ml of 61% by mass nitric acid for each electronic industry) The concentration of metal impurities contained in the polycrystalline silicon rod cut out from the polycrystalline silicon rod was determined in the same manner as in Example 1 except that the final solidified portion was decomposed. The results are also shown in Table 1.

Comparative Example 2
In Example 1, among the polycrystalline silicon rods cut out from the polycrystalline silicon rod, 0.5 g obtained by collecting the precipitation core and surface-etching with hydrofluoric acid was directly accommodated in the bottom of the beaker 5, and the above Example 1 The same operation as in Example 1 was carried out except that the decomposition was carried out in a closed container. From the obtained results, the following calculated concentration (pptw) = (measured value of polycrystalline silicon−operation blank) (pg / ml) × recovered liquid (ml) ÷ 0.5 (g)
Thus, the concentration of metal impurities contained in the polycrystalline silicon rod cut out from the polycrystalline silicon rod was determined. The results are also shown in Table 1.

Example 2
As polycrystalline silicon rods for measuring the metal impurity concentration, three different lots A to C were prepared, and the Cu concentration contained in the polycrystalline silicon rods cut out from these was determined by the same method as in Example 1. . The results are shown in Table 2.

DESCRIPTION OF SYMBOLS 1; Final solidification part decomposition | disassembly airtight container 2; Container main body 3; Sealing lid 4; Final solidification part 5; Beaker 6; Hydrofluoric acid aqueous solution 7; Hot plate 8; Beaker mounting base 9; Heating coil 11; seed crystal 12; silicon single crystal

Claims (8)

A method for measuring the concentration of metal impurities contained in polycrystalline silicon,
Single crystal growth is performed by the FZ method using polycrystalline silicon to be measured, and the final solidified portion is collected from the obtained silicon single crystal rod. Then, the final solidified portion is exposed to silicon decomposable vapor to remove the decomposition residue. A method for measuring the concentration of metal impurities in polycrystalline silicon, which is obtained by dissolving it in a recovered solution, measuring the amount of metal, and converting it to the concentration of polycrystalline silicon to be measured.   2. The method for measuring a metal impurity concentration in polycrystalline silicon according to claim 1, wherein the decomposable vapor of silicon is a vapor of fluoric acid.   The method for measuring a metal impurity concentration in polycrystalline silicon according to claim 1 or 2, wherein the polycrystalline silicon to be measured is rinsed with ultrapure water after etching cleaning.   The method for measuring the concentration of metal impurities in crystalline silicon according to claim 3, wherein the etching solution used for etching cleaning is a hydrofluoric acid aqueous solution.   The metal impurity concentration measurement in the polycrystalline silicon according to any one of claims 1 to 4, wherein the measurement of the amount of metal in the recovered liquid in which the decomposition residue is dissolved is performed by atomic absorption spectrometry or inductively coupled plasma mass spectrometry. Method.  The metal impurity concentration measuring method in polycrystalline silicon according to any one of claims 1 to 5, wherein the metal impurity to be measured is at least one selected from Cu, Ni, and Fe. The method for measuring a metal impurity concentration in polycrystalline silicon according to claim 6, wherein the metal impurity to be measured is Cu.   8. The method for measuring a metal impurity concentration in polycrystalline silicon according to claim 7, wherein the single crystal growth by the FZ method is performed using a silver coil as a high-frequency induction heating coil of polycrystalline silicon.

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